This invention relates to a new process for preparing 4-piperidone spiroketal compounds in excellent yield and purity.
Hindered piperidine alcohol compounds having formula A, which can be named 2,2,6,6-tetramethyl-4-piperidone spiroketal carbinol compounds, or more systematically 9-aza-3-hydroxymethyl-3-alkyl-8,8,10,10-tetramethyl-1,5-dioxaspiro(5,5)und ecanes, ##STR4## have been disclosed by K. Murayama in U.S. Pat. No. 3,899,464 of Aug. 12, 1975 as stabilizers able to protect synthetic polymers and plastics against the harmful effects of exposure of ultraviolet radiation and heat. Compounds of Formula A have also been disclosed to be valuable synthetic intermediates for the preparation of even better stabilizers by reaction of the compounds at the alcoholic hydroxyl group to form various derivatives. Outstandingly effective stabilizers among these derivatives are certain organic phosphite esters disclosed by M. Minagawa et al in U.S. Pat. No. 4,096,114 of June 20, 1978; hydroxyaliphatic dicarboxylic and tricarboxylic acid esters disclosed by M. Minagawa et al in U.S. Pat. No. 4,105,625 of Aug. 8, 1978; diol bis-carbonate esters disclosed by M. Minagawa et al in U.S. Pat. No. 4,115,476 of Sept. 19, 1978; butane-and butenetricarboxylic acid esters disclosed by M. Minagawa et al in U.S. Pat. No. 4,116,927 of Sept. 26, 1978; heterocyclic carboxylic acid esters disclosed by M. Minagawa et al in U.S. Pat. No. 4,118,369 of Oct. 3, 1978; and aliphatic tetracarboxylic acid esters disclosed by M. Minagawa et al in U.S. Pat. No. 4,136,081 of Jan. 23, 1979.
Compounds of Formula I have hitherto been prepared as disclosed by Muraymama by the reaction of a tetraalkyl-4-piperidone with a trimethylolalalkane in the presence of an acid catalyst. However, the procedure has required long reaction times and the product was impure; in Murayama's description of this process no product yields are given.
1,3-Dioxane compounds carrying a hydroxymethyl substituent, l.e. Ketal derivatives of trimethylolalkanes, have been known for some time, but no reactions of such compounds with ketones or aldehydes have been reported. The outcome of any such reaction could not have been predicted, since a ketone or aldehyde could attack at the hydroxymethyl group or at the 1,3-dioxane structure or both of these at the same time.